Rotary disc filters are used to remove suspended solids from water. Influent water flows into a drum and from the drum into a series of disc-shaped filter members secured around the drum. From the disc-shaped filter members, the water flows outwardly through filter media disposed on opposite sides of the disc-shaped filter members. Suspended solids in the water are captured on the interior surfaces of the filter media. From time-to-time, the suspended solids are removed from the interior surfaces of the filter media. This is achieved by rotating the filter media to an upper cleaning position and backwashing the filter media. A pressurized backwash is sprayed onto the exterior surfaces of the filter media, discharging the suspended solids into a trough disposed in the drum. The suspended solids are then discharged from the trough and the disc filter.
To control head pressure in the disc filter, some of the influent water may be diverted from the drum and the disc-shaped filter members. This diverted water is referred to as bypass water. In most cases, the bypass water is directly discharged from the disc filter separately from the disc filter outlet. That is, the bypass water is separately discharged from the disc filter without combining the bypass water with the filtrate in the disc filter itself. This is often a costly solution that is disfavored by end users. In order to implement this solution, one must provide a separate pipe or another concrete channel outside of the disc filter in order to channel the bypass downstream of the disc filter where the bypass water can be mixed with the disc filter effluent or filtered water. A more economical solution is to mix the bypass water with the filtered water in the disc filter, thus bypassing the filtration step itself. However, this presents a backwash problem. Filtered water in the disc filter is typically used for the backwash. Now by mixing the bypass water with the filtered water, there are suspended solids in the filtered water attributable to the bypass water and the suspended solids tend to clog the backwash nozzles and any upstream strainers that are employed to protect the nozzles.
Therefore, there has been and continues to be a need for a rotary disc filter that, in a practical and cost effective way, handles bypass water without suspended solids from the bypass water interfering with the backwash system of the disc filter.